24. Transition Elements

Question 1

Define a transition metal

Answer 1

a d-block element that forms at least one stable ion with a partially filled d-orbital

Question 2

What are the 3 main properties of transition metals?

Answer 2

form compounds in which the transition element has different oxidation states

form coloured compounds

elements and their compounds can act as catalysts

Question 3

Why are transition metals good catalysts?

Answer 3

adsorb other substances onto the surface, as a partially filled d orbital can be used to form bonds to adsorb reactants

Question 4

Write an equation for the Haber process. What is the catalyst?

Answer 4

N2(g) + 3H2(g) => 2NH3(g)

Fe

Question 5

Write equations for the reaction catalysed by Fe2+

Answer 5

(S2O8)2- + Fe2+ => 2(SO4)2- + Fe3+
2Fe3+ + 2I- => I2 + 2Fe2+
thiosulphate ions + iodide ions

Question 6

Write an equation for the reaction catalysed by nickel. What type of reaction is it and what are the other conditions?

Answer 6

C2H4 + H2 => C2H6
+ Ni + 150 C
hydrogenation
produces margarine

Question 7

Write an equation for the reaction catalysed by Cu2+

Answer 7

Zn + H2SO4 => ZnSO4 + H2

Question 8

Write an equation for the Contact Process. What is the catalyst? What does it manufacture?

Answer 8

2SO2(g) + O2(g) => 2SO3(g)
V2O5 catalyst
manufactures sulphuric acid

Question 9

Define a ligand

Answer 9

a molecule or ion that donates a pair of e- to a central metal ion to form a co-ordinate/dative bond (AKA a nucleophile)

Question 10

Define co-ordination number

Answer 10

number of co-ordinate bonds attached to a central metal ion

Question 11

What are the 2 important bidentate ligands?

Answer 11

1,2-diaminoethane (H2NCH2CH2NH2)

ethandioate (C2O4)2-

Question 12

How does a complex ion form in water from a transition metal compound?

Answer 12

water molecules are attracted to the positive metal ion and surround it
transition metals have small size and high charge density therefore they strongly attract ligands like water and NH3

Question 13

Why is there a change in co-ordination number when water ligands are substituted for chloride ions?

Answer 13

chloride ions are too large to fit 6 around a relatively small transition metal ion therefore only 4 bond

Question 14

Name the 4 shapes of complexes, and give an example.

Answer 14

octahedral: most complexes: [Cu(H2O)6]2+
tetrahedral: [CuCl4]2-
square planar: Pt(NH3)2Cl2 (cis-platin)
linear: [Ag(NH3)2]+

Question 15

How do ethandioate ions and 1,2-diaminoethane ions work in complexes?

Answer 15

have an octahedral shape: 3 bidentate ligands each forming 2 co-ordinate bonds: co-ord number = 6

Question 16

What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Cu2+ (aq)?

Answer 16

blue => blue ppt

Question 17

What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Fe2+ (aq)?

Answer 17

pale green => dark green ppt

oxidises to orange-brown in the air

Question 18

What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Fe3+ (aq)?

Answer 18

pale yellow => orange-brown ppt

Question 19

What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Mn2+ (aq)?

Answer 19

pale pink => light brown ppt

Question 20

What is the colour change (i.e. colour of precipitate) when NaOH (or NH3) is added to Cr3+ (aq)?

Answer 20

violet => grey-green

Question 21

What is the colour change when EXCESS NaOH is added to Cr3+ (aq)? What is the formula of the solution formed?

Answer 21

green ppt dissolves to a dark green solution

[Cr(OH)6]3- (aq)

Question 22

What is the colour change when EXCESS NH3 is added to Cu2+ (aq)? What is the formula of the solution?

Answer 22

(pale) blue => deep blue

[Cu(NH3)4(H2O)2]2+ (aq)

Question 23

What is the colour change when EXCESS NH3 is added to Cr3+ (aq)? What is the formula of the solution?

Answer 23

violet => purple

[Cr(NH3)6]3+ (aq)

Question 24

What colour is a solution of Cr3+ if SO4 2- ions are also present?

Answer 24

green

Question 25

What happens when you add conc HCl to to Cu2+ ions in solution? Write the equation.

Answer 25

(pale) blue => yellow

[Cu(h2o)6]2+ + 4Cl- => [CuCl4]2- + 6H2O

Question 26

Why do Cl- ions form complexes with a tetrahedral shape?

Answer 26

the complex ion is more stable

Cl- ions are large and this shape limits repulsion between the ligands

Question 27

Define an optical isomer

Answer 27

compounds with the same molecular and structural formula but which form non-superimposable mirror images of each other i.e. are asymmetric

Question 28

What colour are V2+, V3+ and V4+ respectively?

Answer 28

violet, green, blue